At about 2.20pm on Saturday 23 June 2007 both Sky News and the Daily Telegraph website announced that Alan Johnson had won the election to become Labour's deputy leader. Everything had apparently been going his way following a poll that showed he had a clear enough margin when the results from three parts of Labour's electoral college were aggregated.

As it turned out they were wrong. For none of the pundits or pollsters had fully thought through how the voting system that applied in each segment would work, and how important the second and third preferences were. To the surprise of virtually everyone, Harriet Harman took the crown. So predicting the coming five-sided contest with three different electorates and a complex voting system is going to be challenging.

A key factor will be how the movement feels about itself and what it is looking for during the second week in September, when the ballot papers go out. It is still less than a month since Gordon Brown left Downing Street, and Labour has yet to absorb fully the fact that it is now in opposition. All sections of the electoral college will be looking for a contender best able to fight the Tories and the coalition.

On top of this there will be at least one TV debate between the five hopefuls. Following the general election debates, being able to perform in such an arena will be seen as central. Here, I think that Andy Burnham and Diane Abbott could be the surprises. During the election a TV producer told me that she thought Burnham had "killer eyes", while Abbott, of course, has probably more TV experience than any of them with her regular appearances on the BBC's This Week.

Based on the number of MP nominations he's accumulated David Miliband looks set to win the MP section. You can see him and his brother, Ed, doing well with the party membership, while Ed Balls will surely do well among trade unionists.

All of this will be in the context of the big political story that should run right through the campaign: the coalition's cuts package. Here, Ed Balls looks best placed to show his prowess, for he holds the schools portfolio which should provide opportunities for him to demonstrate his battling qualities. The Miliband brothers, in contrast, cover climate change and foreign affairs, which are not as central to the big argument.

So who will win? The David Miliband campaign has a lot of momentum and he is going to be hard to beat, but I would not be surprised if it was the combative Ed Balls who gets the prize. But Diane may yet secure lots of second preference votes from women, while Andy Burnham is not as well known as the other four, and has fewer enemies.